Process for injecting thermal fluids for food processing

ABSTRACT

A process for internally cooking food includes the steps of injecting a condensable cooking fluid into the interior of the food at a plurality of spaced-apart locations, dispersing the cooking fluid within the interior, and condensing the cooking fluid while in direct contact with the interior. The heat of condensation of the cooking fluid releases considerable heat energy useful for either pre-cooking the food to a desired intermediate cooking level, or thoroughly cooking the food. The heat of condensation of the fluid is high enough that only a small amount of condensable cooking fluid is required, per quantity unit of food being cooked. As a result, the food does not become excessively loaded with cooking fluid, and flavorants such as marinade substantially remain within the food. Where the condensable fluid is used for pre-cooking, the cooking may be thoroughly completed by placing the pre-cooked food in a conventional hot air oven. The pre-cooking or thorough cooking of food using properly injected condensable cooking fluid, considerably reduces the total cooking time compared to conventional oven cooking.

RELATED APPLICATIONS

[0001] This patent application claims priority based on U.S. ProvisionalApplication Serial No. 60/168,328, filed on Dec. 1, 1999.

FIELD OF THE INVENTION

[0002] This invention relates to a method and apparatus for cooking foodusing the heat of condensation from a condensable inert gaseous fluidthat is injected directly into the interior of the food. As used herein,the term “cooking” includes partial cooking or pre-cooking, and is notlimited to complete or total cooking. The term “injected” requiresdirect surface contact between the condensable fluid and the interior ofthe food. Fluid which is passed in and out of the food through arecirculating tube without touching the food, is not “injected” as theterm is used herein.

BACKGROUND OF THE INVENTION

[0003] In today's fast-paced economy, consumers are relying more thanever on pre-packaged, prepared meals and meal items which can be madeready to eat by heating in a microwave or conventional oven for a shortperiod of time. The phrase “prepared meals and meal items” refers toentire meals, and meal entrees, which are prepared and cooked by amanufacturer, packaged, often frozen, and sold to consumers in a formalmost ready for consumption. Spurred by the high consumer demand, thequality, variety, and number of brands of prepared frozen meals and mealitems have risen in tandem. Markets for prepared meals and meal itemshave expanded to include special child and toddler meals, restaurantmeals, and hospital meals as well as typical adult meals.

[0004] One strict requirement for prepared meals and meal items is thatthey be totally safe for consumption. Among other things, the meals andmeal items must be thoroughly cooked by the manufacturer prior tofreezing and shipping. The short preparation times tolerated by theconsumer, along with the uneven heating provided by microwave ovens andvariations between different ovens, preclude reliance on the consumer toaccomplish any part of the required cooking.

[0005] Because of uneven heating and other complications, manufacturerstypically have not relied heavily on microwave ovens to accomplish therequired internal cooking. More often manufacturers rely on large,conventional hot air or impingement ovens (sometimes employing moistair) to cook the food products from the outside in. When cooking poultryand meats, especially those containing bones, the cooking times requiredfor hot air or impingement ovens can be quite long. Manufacturers havesought to reduce this cooking time using a variety of pre-cookingtechniques.

[0006] One particular challenge is to cook bone-in products such aspoultry, to an extent needed to eliminate any redness in the vicinity ofthe bone. This requires thorough cooking of the bone, often to 180° F.or higher. To achieve thorough cooking of the bone from the outsideusing a convection oven may result in excessive cooking of the surfaceportions of the food product and/or excessive cooking times. There is aneed for a technique for cooking the bones and surrounding regionswithout excessively cooking the remainder of the food product.

[0007] In one pre-cooking technique, a hot gas such as air can beinjected into the interior of the food using a plurality ofclosely-spaced injection nozzles or needles. The hot air can be injectedat sufficient pressure, volume and temperature to elevate the interiorof the food from a lower temperature to a desired higher temperatureprior to placing the food in an oven, thus reducing the required cookingtime in the oven. However, the heat capacity of air is quite lowcompared to the heat capacities of the solid and liquid-containing foodsbeing heated. Accordingly, the amount of energy released by taking airfrom a higher to a lower temperature, and/or from a higher to a lowerpressure, is low enough that a high volume of the air may be required toelevate the food temperature by any desired amount. The injection of toomuch hot air can cause unwanted drying of the food.

[0008] In another pre-cooking technique, a hot aqueous liquid can beinjected into poultry or meat to raise its internal temperature. Thistechnique has an advantage in that the heat capacity of the liquid beinginjected is much closer to the heat capacity of the food being heated.On the other hand, the quantity of liquid being injected is quitelimited by the need to avoid over-saturation and/or excessive rinsing ofthe food.

[0009] In another pre-cooking technique, a plurality of closely-spaced,recirculating heat exchanger needles can be planted in the food, and ahot recirculating fluid (liquid or gas) can flow through the needles sothat heat is transferred to the food through thin, heat-exchanger typeneedle walls. This technique has an advantage in that there is no directcontact between the heating fluid and the food. However, because thefluid cannot penetrate the food, the portions of food immediatelyadjacent to the heat exchanger walls may be heated to a greater extentthan portions of the food away from the needles, resulting in unevencooking.

[0010] There is a need or desire in the food industry for a process forcooking food from the inside which is uniform, efficient, and does notresult in over-exposure of the food to a cooking fluid.

SUMMARY OF THE INVENTION

[0011] The present invention is directed to a process for cooking foodfrom the inside which achieves the desired level of cooking using acondensable cooking fluid, which condenses from a gaseous to a liquidstate while in direct contact with the food. As used herein, the term“condensable cooking fluid” refers to a fluid which undergoes a phasetransition, from gas to liquid, at a temperature between about 100-450°F. at the pressure (if any) used for cooking. The heat of condensationof the fluid provides the heat that is needed to heat and cook the food.Because the heat of condensation is much larger than the amount of heatreleased by simply cooling a gas or a liquid from a higher temperatureto a lower temperature, a much lower quantity of the condensable fluidis required, per pound of food being cooked, than would be required ifthe fluid did not undergo a phase transition from gas to liquid.

[0012] In accordance with the invention, the condensable cooking fluidis injected directly into the food at a plurality of (two or more)spaced apart locations, and the fluid cooks the food as it condensesinside the food. The quantity of condensable cooking fluid, per pound offood being cooked, is carefully controlled so as to heat the food from aknown lower temperature to a desired higher temperature. The pressure ofthe fluid being injected is controlled so as to sufficiently diffuse thecondensable cooking fluid within the food (i.e., away from the injectionports) to uniformly cook the food, without permitting excessive fluid toescape from the food before it condenses, and without causing excessivebleeding of flavorants such as marinade from the food. The product yieldis thus maximized. The injection points or ports are spaced sufficientlyclose together so that the condensable fluid can diffuse and uniformlycook the food.

[0013] The process of the invention is particularly useful for theinternal pre-cooking of frozen meals and meal items, including bone-infood products, with the final cooking step being accomplished by aconventional hot air or impingement oven. The process of the inventioncan also be used to thoroughly cook food items. The condensable cookingfluid is preferably inert to the food being cooked, and must be safe forconsumption when cooled. One particularly useful condensable cookingfluid is steam. Steam is useful for the cooking of prepared meals andmeal items, including larger multiple-serving meal items (turkeys, hams,roasts and the like) as well as individual meals and meal items.Condensing steam is also effective in cooking bones and surroundingregions, thus eliminating any redness in the final product. Generally,the quantity of condensable fluid used is sufficiently low so as not tomaterially affect the weight of the food product.

[0014] With the foregoing in mind, it is a feature and advantage of theinvention to provide a process for internally cooking foods which uses afairly low amount of condensable cooking fluid per pound of food beingcooked.

[0015] It is also a feature and advantage of the invention to provide aprocess for internally cooking foods which performs an effective amountof cooking through direct contact between the food and an inertcondensable cooking fluid, without adversely affecting the food quality.

[0016] It is also a feature and advantage of the invention to provide aprocess for internally cooking foods which uniformly cooks the food to adesired level, and which eliminates any redness in the vicinity ofbones.

[0017] It is also a feature and advantage of the invention to provide aprocess for internally cooking foods which does not cause excessiveescape of marinades and/or other internal flavorants from the food,thereby maximizing product yield.

[0018] It is also a feature and advantage of the invention to provide anintegrated process for pre-cooking food using an inert condensablecooking fluid, and completing the cooking using a hot air or impingementoven, which results in energy savings, time savings, and improvedproduct yield compared to current industrial cooking processes.

[0019] The foregoing and other features and advantages of the inventionwill become further apparent from the following detailed description ofthe presently preferred embodiments, read in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a block diagram of an exemplary food product cookingsequence, including the step of pre-cooking by condensable fluidinjection in accordance with the present invention;

[0021]FIG. 2 is a side elevational view of a fluid injector apparatususeful in practicing the present invention;

[0022]FIG. 3 is a front elevational view of the fluid injector apparatusof FIG. 2;

[0023]FIG. 4 is a perspective view of the manifold and plurality ofneedles of the apparatus of FIG. 2;

[0024]FIG. 5 is a cross-sectional view of the plurality of needlespenetrating the interior of a bone-in food product;

[0025]FIG. 6 is a block diagram of an exemplary food product cookingsequence including the step of using a vision system to facilitateprocessing of the food product to the fluid injector apparatus inaccordance with the present invention;

[0026]FIG. 7 is a front elevational view of an alternate embodiment ofthe invention showing a dual conveyor and dual injection system;

[0027]FIG. 8 is a block diagram representation of a food product cookingsequence where food products are fully cooked directly after thepre-cooking in accordance with the present invention;

[0028]FIG. 9 is a side elevational view showing the fluid injectionapparatus in phantom within a conventional convection oven;

[0029]FIG. 10 is an alternate configuration of a continuous rotatinginjector manifold;

[0030]FIG. 11 is a side elevational view of an injector needle;

[0031]FIG. 12 is a bottom plan view of the apparatus, showing anarrangement of closely spaced fluid injection needles;

[0032] FIGS. 13(a), 13(b) and 13(c) are schematic views showing threealternative pattern arrangements for the fluid injection needles.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0033]FIG. 1 is a schematic illustration of one example of an integratedprocess for cooking prepared meals and meal items. A food product isloaded on a conveyor belt 12. The conveyor belt transports the foodproduct to a fluid injector 14 where the food product is pre-cooked bycondensable fluid inserted into the food product. If the food product isto be breaded, the food product is then passed to a dusting station 16,a battering station 18, and a breading station 20. At this point thefood product may optionally be subjected to a frying station 22. Thefood product is then conveyed to the hot air oven 24 where the cookingis completed. The food product is then frozen at station 26 and packagedat station 28 for delivery to the customer.

[0034] A fluid injection apparatus 10 useful for injecting thecondensable fluid, is shown in FIGS. 2 and 3. FIG. 2 is a sideelevational view of the apparatus and FIG. 3 is a front elevational viewof the apparatus with the housing removed. The apparatus 10 includes asupport frame 30 and a housing 32 with a product inlet 36 and a productdischarge outlet 38. A conveyor belt 40 transfers the food product 42through the housing 32.

[0035] The apparatus 10 includes an injection manifold 44 having aplurality of needles 46 extending downward therefrom and perpendicularto the conveyor belt 40. The needles 46 are fluidly connected throughthe manifold 44 to an inlet 48 connected to a pump and a source of fluid(not shown). The manifold 44 is connected to a carriage 52 which iscapable of moving the manifold 44 vertically to a plurality of up anddown positions. The food product 42 is placed on the conveyor belt 40,and is conveyed beneath an inlet guard 54 which ensures that any foodproduct 42 which is either too big or stacked upon itself will beprevented from entering the housing inlet 36.

[0036] The conveyor belt 40 stops when the food product 42 is directlybeneath the manifold 44. The carriage 52 forces the manifold 44 downwardsuch that the plurality of needles 46 are inserted to a depth generallycorresponding to the center of the food product 42. A condensable fluid,preferably culinary or sanitary steam made from pure (e.g., filtered)water, is introduced into the interior of the food product. The carriage52 can be carried on each side by a piston rod 53 telescopicallyengaging a piston shaft 55. Each piston rod 53 may be drivenpneumatically, or with springs, or with fluid pressure applied insidethe shaft 55. The condensable fluid is injected into the food product 42through the injection needles 46 under pressure from the source (notshown).

[0037] The steam contacts the interior of the food product 42, which isat a lower temperature. This causes the steam to condense, releasingheat energy as the steam undergoes a phase change. Because there is aphase change, heat transfer from the fluid to the food product may occurwithout substantially changing the temperature of the fluid. The latentheat energy of the vapor has a heat transfer coefficient and rate whichis generally much larger than those characteristic of convection heattransfer without a phase change. The use of a condensable fluid allows amaximum amount of energy to be injected into the interior of the foodproduct 42 while minimizing the volume of the residual fluid remainingin the food product 42.

[0038] Once the fluid has changed phase into a liquid, the heat energycontinues to be transferred into the interior of the food product byconduction. The condensed fluid continues to transfer heat into theinterior of the food product 42 until the temperature thereof and theinterior temperature reach equilibrium. The amount of condensable fluidand injection time will vary based upon the particular food productsbeing treated and the desired end point temperature for the productinterior.

[0039] Once the steam is injected into the food product 42, the manifold44 is elevated to retract the needles 46 from the food product 42. Astripper 58 is positioned between the food product 42 and the needles 46to prevent the food product 42 from sticking to the needles 46. Thestripper 58 may include a plate having a plurality of openings whichenable the needles 46 to be extended and retracted through the platewhile preventing the food product 42 from sticking to the needles 46.The conveyor belt 40 then moves the food product 42 out of the housingto allow processing of the food product 42 to continue.

[0040] In some applications, the apparatus 10 will be used to pre-cookor partially cook food by bringing its internal temperature from a lowerrefrigeration temperature of about 32-45° F. to a higher cookingtemperature of about 80-130° F., with the final cooking step occurringin a downstream hot air oven (which further elevates the foodtemperature to about 160-210° F.). When steam is employed as thecondensable cooking fluid, this pre-cooking can be accomplished using afluid injection rate of about 0.01 to 0.25 pounds of steam per pound offood being cooked, typically about 0.02 to 0.15 pounds of steam perpound of food being cooked, suitably about 0.03 to 0.08 pounds of steamper pound of food being cooked, desirably about 0.04 to 0.07 pounds ofsteam per pound of food being cooked. The fluid quantities will varydepending on the type of food being cooked and the amount of cookingdesired. To elevate poultry from a refrigeration temperature of 32-35°F. to a pre-cooking temperature of 110° F. requires about 0.054-0.065pounds of steam per pound of poultry being cooked.

[0041] One advantage of pre-cooking the food to an intermediatetemperature of 80-130° F. or, more suitably 90-120° F., is that theamount of steam required is not so large as to cause excessive bleedingof marinade and/or other flavorants. Yet, the elevation in temperatureis sufficient to enable a substantial reduction in downstream cookingtime in the hot air or impingement oven, particularly for bone-in andlarge food items such as turkeys, roasts and hams. In effect, theoverall product yield (which is a function of cooked product quantityper unit time and percentage of acceptable product) can be optimizedwith these steam quantities and pre-cooking temperatures.

[0042] The steam or other condensable fluid should be injected undersufficient pressure to allow substantial penetration of the fluid intothe product being cooked, but not so much pressure that excessive fluidescapes (e.g., percolates) from the food product before it condenses.Preferably, the steam is injected as superheated steam. To ensureoptimum results, the steam should be injected at a pressure of about5-50 psig., suitably about 10-40 psig, desirably about 20-30 psig. Steaminjection at a pressure of 23-28 psig (corresponding to a saturatedsteam temperature of 263-271° F.) is preferred for meat and poultryapplications.

[0043] Another important variable is the needle density, i.e., thenumber of injection needles 46 per unit area. Preferably, the needlesare uniformly spaced apart. If the needle density is too low, then it isdifficult for the steam to uniformly penetrate and cook the food. If theneedle density is too high, then the overall steam quantity (at a givenpressure) is high, and higher energy is required to press the needlearray into the product. Useful needle densities may range from about1-30 needles per square inch, suitably about 3-25 needles per squareinch, desirably about 5-20 needles per square inch.

[0044] Exemplary arrangements of needles 46 are shown in FIGS. 13(a)through 13(c), in which needles 46 are represented by points. Thecircles surrounding and/or connecting the needles help illustratedifferent needle patterns, but are not otherwise indicative ofstructure. FIG. 13(a) represents a desired pattern for a lower level ofneedle density, ranging up to about 5 needles per square inch. FIG.13(b) represents a desired pattern for a somewhat higher needle density,ranging from about 5-10 needles per square inch. FIG. 13(c) represents adesired pattern for a still higher needle density, ranging from about10-20 needles per square inch and possibly higher.

[0045] Another variable is the residence time of the needles in the foodproduct, which generally corresponds to the cycle time required tocomplete the steam injection. Normally, the desired amount of steam canbe injected in about 1-60 seconds, suitably about 2-30 seconds,desirably about 3-10 seconds. At 5 seconds, for instance, the steaminjection residence time is about 0.55% of a typical oven cook time of15 minutes, illustrating the time efficiency of using condensing steamto help cook the food. Preferably, the steam is injected continuouslywhile the needles are being extended into and retracted from the foodproduct. This way, portions of the steam are injected at differentelevations within the food product, facilitating more uniform cooking ofthe food. Alternatively, all of the steam may be injected when theneedles are stopped at a desired level within the food product.

[0046] Referring again to FIGS. 2 and 3, the needles 46 may beconfigured with a single injection opening 47 located at a lower end ofeach of the needles. Alternatively, the injection opening 47 may bealong a side of each of the needles, and/or each needle may have morethan one injection opening 47. Each needle 46 has a penetration lengthand indexing time sufficient to allow the desired level and time ofpenetration into the food product being cooked. Depending on theapplication, the needles 46 may have penetration lengths of about 0.5-10inches, suitably about 1.0-5.0 inches, commonly about 1.5-3 inches. Theoverall length of each needle is typically longer than the length whichpenetrates the food, so that steam may be fed into each needle at alocation along the needle which remains outside of the food. Needlelengths may be about 4-8 inches longer than the portion which enters thefood.

[0047] The term “index length” refers to the length of each cycle, i.e.,the distance that the food conveyor underneath needles 46 travelsbetween each penetration, injection and retraction cycle of the needles46. Depending on the application, the index length is generally about1-12 inches, more typically about 4-8 inches. When the index length isvery short, a single meal or meal item may experience steam injectionmore than once as it passes beneath needles 46.

[0048] The needles 46 may be individually biased with respect to themanifold 44 to permit variable insertion levels for different needles.For instance, if it is desired to insert the needles 46 by 6 inches intoa product, and if some of the needles are stopped after two inches ofinjection because they interact with a hard bone, the remainder of theneedles should be permitted to penetrate by the desired level of depth.By having the needles 46 individually biased with respect to manifold44, the remainder of the needles 46 may reach the desired depth eventhough one or more needles have been interfered with at a higherelevation. The individual bias may be accomplished by pneumaticallyloading and driving needles 46 at a first end opposite the injectionopenings 47. The biasing pneumatic load may range from about 1-50 psig,suitably about 2-30 psig, commonly about 5-15 psig depending on theapplication. If the pneumatic load is too high, the needles 46 maypenetrate and damage bones and other hard objects in the food product.If the pneumatic load is too low, the needles 46 may insufficientlypenetrate even the soft portions of the food product.

[0049] The first side and opposing second side of a food product may becooked separately, for instance in separate stages. In one alternateembodiment as shown in FIG. 2, the apparatus 10 includes a secondmanifold 50 having a second plurality of needles 51 located underneaththe conveyor belt 40, for injecting the food product 42 with steam fromthe reverse side of the food product 42. When using a second manifold50, the needles 51 must protrude through the conveyor belt 40. It isalso contemplated that the stripper 58 can be lowered onto the foodproduct 42 on the conveyor belt 40 to provide a backing such that thefood product 42 is properly held in place when the needles 46 and 51 ofthe manifolds 44 and 50 are inserted into the food product 42.Alternatively, a second stripper 58 may be located below the conveyorbelt 40. It is contemplated that injection needles will be manipulatedto introduce the condensable cooking fluid at or near the center of thefood products, as this is the primary region to be pretreated. Thevertical movement of the needles may thus be controlled to accomplishthis objective, depending on the characteristics of the food products.

[0050] In another alternative embodiment, both sides of the food productmay be treated using the first assembly of manifold 44 and needles 46shown in FIGS. 2-4, or two similar injection assemblies located on thesame side of the conveyor belt 40. Initially a first side of the foodproduct is treated with steam by lowering injection needles 46 into theproduct. After the injection is completed, the food product is flippedover whereupon a second side of the food product is steam treated usingthe same or a different set of needles 46 mounted to the same or adifferent manifold 44.

[0051] The conveyor belt 40 may also have a plurality of holes (notshown) which are positioned and timed to allow the needles 46 to passthrough the conveyor belt 40 if the injection needle design introducesthe thermal fluid into the food products above the tip of the needles.The conveyor belt 40 is designed to have sufficient rigidity towithstand the force created when the upper manifold 44 pushes down onthe food product when injecting its needles 46. Alternatively, a supportcan be used beneath the conveyor belt 40 to provide the requiredstructural integrity for the injection process.

[0052] Turning now to FIG. 4, a perspective view of an injector manifold44 is shown positioned over a conveyor belt 40. The plurality of needles46 are shown forming a flock of injectors having a predetermined widthand depth. The amount of needles 46, the density of the needles 46 perarea, and the length of the needles 46 are all predetermined inaccordance with the intended use of the apparatus 10, the types of foodproducts to be treated, and the level of cooking desired. FIG. 12 is abottom plan view of the needle arrangement shown in FIG. 4, wherein theneedles 46 are arranged in a pattern as shown in FIG. 13(b), discussedabove. The entire array of needles 46 shown in FIG. 12 includes 280needles. Such a large array of needles 46 can be used to cook a largefood item, for instance a large turkey, roast or ham. Smaller needlearrays (having fewer needles) may be used to cook individual meals andmeal entrees. Alternatively, a large array of needles (as shown in FIG.12) may be used to cook several smaller meal items, placed side by side,at the same time.

[0053]FIG. 5 depicts a partial cross-sectional view of a bone-in foodproduct 42 on a conveyor belt 40 being injected by needles 46 of aninjector manifold 44. The individual needles 46 project into the foodproduct 42 until they encounter a bone 62 which stops their downwardmotion. It is contemplated that each needle 46 will extend to apredetermined depth if it does not encounter a bone 62. Thepredetermined depth preferably corresponds to the center of the foodproduct 42. The individual hinging of needles 46, described above,allows the needles to reach varying depths. It is also contemplated thatthe targeted depth for each needle can be determined for each foodproduct individually. The apparatus 10 may be configured to sense whenthe needles 46 are inserted into the food product, and calculate thelocation of the center of the food product in relation to the conveyorbelt height and the entering height of the needles 46.

[0054] Referring now to FIG. 6, another integrated process for cookingprepared meals and meal items is schematically shown. A food product isloaded on a conveyor belt 12. A vision system 64 is provided with thecapability to identify the configuration of the food products, such assize, thickness or the like on the conveyor 12. The identified foodproducts may then be segregated at station 66 onto different belts orpaths A and B, according to their configuration as detected by thevision system. The conveyor belt A transports the first selected foodproducts to individually controlled fluid injection systems where eachselected food product is pre-treated by a condensable fluid insertedinto the food product by the fluid injection system 14. In this manner,products having similar characteristics can be processed together toachieve desired results. If the food is to be marinated or otherwiseflavored, the flavorant may be injected before or after the condensablefluid at flavoring station 11, and is preferably injected before thecondensable fluid as shown.

[0055] The conveyor belt B takes the second selected food productsthrough a processing 23 which may or may not include the same processingstations and steps as described for the first selected food products onconveyor belt A. For instance, a chicken may be separated into breastsand thighs on belt A which are subject to pre-cooking, and wings anddrums on belt B which may not require pre-cooking due to their smallersizes. When the breasts, thighs, wings and drums reach the oven 24, theymay experience the same cooking time which is sufficient to a) fullycook the wings and drums, and b) finish the cooking of the breasts andthighs. This way, overcooking of the smaller items is avoided, and theoverall product yield is optimized.

[0056] The segregation of the food products in this way would also allowseparate injection systems to be used to increase the volume ofcondensable fluid or dwell time for the larger pieces and/or decrease oreliminate these variables for the smaller pieces. This will ensure moreheat energy is transferred to the larger pieces. The volume ofcondensable fluid, dwell time or other processing characteristics can becontrolled by a control system 68, and in this embodiment in conjunctionwith the vision system 64, to optimize the processing characteristicsbased on the sizes or other characteristics of the food products. Again,if the first selected food product is to be breaded, the food product isthen pre-dusted at station 16, battered at station 18, and breaded atstation 20. At this point the food product may optionally be subjectedto a frying step at station 22. The food product is then conveyed to theoven where the food product is fully cooked at convection oven 24. Thefood product is then frozen at station 26 upon removal from the oven andpackaged at station 28 for delivery to the customer. These processingsteps may or may not be included, or may be performed differently, forthe second selected food products on belt B.

[0057] Turning now to FIG. 7, a dual conveyor injector apparatus 100 isshown in a front elevational view. The vision system 110 is shown abovethe apparatus 100. The vision system 110 can be any system that candetect and identify moving objects and provide control signals to eithersort the detected objects based on a specific criteria, or to controloperation of the apparatus 100, or both. The vision system 110 can bedesigned to provide signals directly to the apparatus 100 to controlitems such as injection dwell time and injection depths for individualneedles in the system. In the preferred embodiment, the apparatusincludes two or more conveyor belts 140 and two or more injectionmanifolds 144 each connected to an inlet 48 and a plurality of needles46. The manifolds are supported and controlled by carriages 152 attachedto the frame 130 of the apparatus 110. The apparatus also comprisesinlet guard 54 and stripper plate 58.

[0058]FIG. 8 schematically illustrates a simplified integrated processfor cooking prepared meals and meal items, where a breading step is notneeded. This process may be used to cook large turkey parts, hams,roasts, beef sections and the like. Such products are difficult to fullycook in a convection oven, without the aid of steam injection, becausetheir large interior portions cannot be adequately cooked in areasonable time, particularly if bones are present. The food productsare placed onto the conveyor belt 12 and transported to the fluidinjection apparatus 14, where the large food products are pre-cooked.Desirably, the large food items may be subjected to pre-cooking by bothan upper needle injection manifold 44 and a lower needle injectionmanifold 50, as explained above with respect to FIG. 2. The dwell timeand/or amount of fluid injected will be proportionately increased toaccount for the larger mass of these food products. The density of theneedles 46 and 51 per unit area may also be increased in the manifolds44 and 50. It is preferred that the steam be injected at a predeterminedrate during the extension and retraction of the manifolds 44 and 50 suchthat the needles 46 and 51 inject steam from the time they firstpenetrate the food item, throughout their downward or upward movement inthe food product. To conserve condensable fluid, the apparatus may becontrolled to only inject when the needles 46 and 51 are in contact withthe food products. This will provide more heat energy and facilitate thepre-cooking process by contacting more area of the interior withcondensable fluid. The food products are then directly conveyed to aconvection oven 24 where they are fully cooked, then frozen at station26 and packaged at station 28 for delivery to the retailer or end user.

[0059] Although the fluid injection apparatus 10 has been shown as astandalone unit, the apparatus can be made as an integral part of aheated air convection oven. Referring now to FIG. 9, the fluid injectorapparatus 10 is shown within a convection oven 200 having multiplecooking stages 202, 204, 206 and 208. The apparatus 10 is mounted in thefirst stage 202 of the oven 200 such that the food product entering theoven 200 is pre-cooked by the apparatus 10 and then fully cooked in theremaining stages 204, 206 and 208. If steam is used as the condensablecooking fluid, the introduction thereof into the oven housing will alsofacilitate the cooking operation as steam is conventionally introducedinto such ovens to maintain the moisture content of the food productsduring cooking.

[0060] The operation of the convection oven 200 is otherwiseconventional, and need not be discussed in detail. Briefly,recirculating hot air (preferably directly or indirectly heated bynatural gas or another fossil fuel) enters the lower part of oven 200 atthe final stage 208, so that the final stage 208 is the hottest part ofthe oven. The hot air passes through the stages 206, 204 and 202, andexits through outlet 201. The hot air cools somewhat as it heats andcooks the food product, thus rendering the first cooking stage 202 thecoolest part of the oven. Some of the hot air is exhausted through ports201 and 209, and a corresponding amount of room air is drawn in with thefood, or separately.

[0061] The air temperature within the oven, and the hot air flow rates,are selected so as to finish the cooking of the food product. Each foodproduct must be cooked to an elevated internal temperature which is atleast high enough to meet food safety requirements. Poultry, forinstance, must be thoroughly cooked to at least 160° F. according toHazard Analysis Critical Control Point (HACCP) requirements, meaningthat each and every part of the poultry must reach or exceed thattemperature. To accomplish this, and allow a safety margin, thetemperature in the final stage 208 of the oven 200 may be set to reach180-200° F. As explained above, the residence time of the food in theoven 200 may be on the order of 15 minutes, or may be shorter or longerdepending on the type and size of the food articles being cooked. Theresidence time and heat supplied must be sufficient to assure that allportions of the food reach or exceed the required U.S.D.A. temperaturefor total elimination of bacteria.

[0062]FIG. 10 illustrates another embodiment of a fluid injectionapparatus, specifically a continuous injection manifold 240, which caneffectively pre-cook the food items without repeatedly starting andstopping the underlying conveyor. The continuous injection manifold 240incorporates a rotating injection manifold 244 including a rollstructure (wheel or drum) 242 rotatable about a center 254. A pluralityof injection needles 246 project from an outer periphery of manifold 244at an angle which is generally orthogonal to the circumference of theroll 242. The roll is supported and positioned at a predetermined heightin relation to the conveyor belt 40. Food product 42 on the conveyorbelt 40 is pierced by the plurality of needles 246 as the food product42 passes underneath the wheel 242.

[0063] The wheel 242 has an inlet 248 for intake of condensable cookingfluid, which is forced under pressure through a stationary manifold 250and into the rotating manifold 244. The manifold 250 is sealed againstthe interior surface 252 of the wheel 242. The needles 246 have inlets(not shown) projecting through the wheel 242 such that when the needles246 are beneath the manifold 244 the pressurized cooking fluid is forcedthrough the needles 246 and injected into the food product 42. As in theprevious embodiments, the condensable cooking fluid, desirably steam,condenses and releases heat energy as the vapor changes into a hotliquid. Because there is a phase change, much of the heat transfer fromthe fluid to the food product 42 occurs without changing the temperatureof the cooking fluid.

[0064] Once the cooking fluid has changed phase into a liquid, the heatenergy continues to be transferred into the interior of the food product42 by conduction until the cooking fluid and the interior of the foodproduct 42 are at equilibrium temperature. As with the manifolds 44 and50 of the previous embodiments, the length and density of the needles246, the size and width of the roll 242 as well as speed of rotation,and the dwell time and/or volume of fluid injected are controlled inrelation to the speed of the conveyor belt 40 to optimize the cooking ofthe food product.

[0065] Referring now to FIG. 11, a preferred fluid injection needle 46,246 of the present invention is shown. The needle 46, 246 includes ahollow metallic shaft 202 having a piercing end 206 terminating in apoint 204. The body 202 has one or more apertures 208 near the piercingend 206, in addition to the main aperture 47 at the piercing end. Theseadditional apertures allow for a larger area of the interior of the foodproduct 42 to be subjected to the condensable cooking fluid immediatelyfollowing injection. The needle 46, 246 is strong enough to withstandrepeated contact with a bone of a food product 42 without damage. Whenthe needle 46, 246 has a plurality (for example, four, six or eight)apertures 208 along its shaft 202, all of the apertures 208 should bepositioned within the food product during steam injection. If some ofthe apertures 208 are not within the food product, the steam will tendto exit through those openings, reducing the effectiveness of thecooking.

[0066] The foregoing process and apparatus for cooking food with acondensable fluid provides a unique arrangement of process steps andcomponents to allow a relatively small amount of fluid to be injectedinto the interior of a food product, to achieve time and energy-savingpre-cooking of the food. The invention overcomes limitations withrespect to the amount of heat energy transferred to the food product,and especially to the center or bone area of bone-in food products. Theability to use the process and apparatus in conjunction with visionsystems, product segregation and multiple manifolds enables optimizationof the pre-cooking and cooking operations. The use of a continuousrotating manifold allows the conveyor belt to operate non-stop. Theprocess and apparatus also provide the ability to pre-cook large foodparts which typically cannot be economically cooked in a conventionalconvection oven. These and the other characteristics of the fluidinjection process and apparatus provide a high confidence, efficient andversatile system which pre-cooks the injected food from the inside-out,and then from the outside-in using a conventional oven. The apparatusallows the food product to be subjected to less time and thermal energyin the conventional oven while achieving interior temperatures above theUSDA minimum. The apparatus is versatile enough to be used in line alongwith other processing equipment or as an integral part of a conventionaloven.

[0067] The foregoing descriptions of preferred embodiments of theinvention are merely examples, and the invention is not to be limited tothe preferred embodiments, as many variations or modifications would beapparent to those skilled in the art based upon the principles of theinvention as set forth herein. Such variations or modifications arecontemplated within the scope of the invention as set forth in theappended claims.

We claim:
 1. A process for heating food from a first lower temperatureto a second elevated temperature, comprising the steps of: injecting acondensable cooking fluid into an interior of the food; and convertingthe condensable fluid from a gaseous phase to a liquid phase while indirect contact with the interior of the food; wherein the condensablefluid is injected in an amount of about 0.01 to about 0.25 pounds ofcondensable fluid per pound of food being heated.
 2. The process ofclaim 1, wherein the condensable fluid comprises steam.
 3. The processof claim 1, wherein the first lower temperature is about 32-45° F. 4.The process of claim 3, wherein the second elevated temperature is about80-130° F.
 5. The process of claim 3, wherein the second elevatedtemperature is about 90-120° F.